An attempt to understand dissolved air flotation using multivariate data analysis

Milos Krofta, Banda Herath, David Burgess and Larry Lampman

ABSTRACT
In order to optimize the dissolved air flotation (DAF) process, a mathematical relationship should be established between the operating variables and the quality of the effluent water. In this study, operating parameters, including influent wastewater characteristics, were related to suspended solid (SS), COD, BOD5 and turbidity of the effluent via an empirical mathematical model.

The data presented in this study were obtained from a pilot plant DAF study carried out on municipal wastewater at Lee, Massachusetts to determine the operating conditions for the wastewater clarification. Response surface methodology was used to determine optimal conditions and to study the variations of flotation behaviour with varying operating conditions.

The multivariate technique used in this study is an extremely valuable tool to analyze data obtained from actual wastewater treatment processes where the characteristics of the wastewater are constantly changing. Without such a tool it may not be possible to draw valid conclusions. In addition, this technique requires comparatively fewer experiments when compared to traditional methods.

Addition of more flocculant and recycle water over what is required actually decreases the effluent water quality. Tests carried out with the same DAF unit at Little Rock, Arkansas and Birmingham, Alabama have confirmed the accuracy of the predictions from the model.